Monolithic molded flexible electronic assemblies without solder and methods for their manufacture

ABSTRACT

A method ( 10 ) for manufacturing a monolithic molded electronic assembly ( 12 ). A mold ( 14 ) having first and second mold potions ( 14   a - b ) that mate to form an interior chamber ( 16 ) is provided. The mold has an injection port ( 22 ) and channel ( 24 ) connecting into the chamber. Electronic parts ( 30 ) having electronic contacts ( 32 ) are populated onto the second mold portion, to be substantially contained in the chamber. The mold potions are mated together and a liquid insulating molding material ( 36 ) is injected through the injection port channel to fill the chamber. The molding material is hardened to a solid, thereby embedding the electronic parts in the molding material as a monolithic sub-assembly ( 40 ). The monolithic sub-assembly is removed from the mold and one or more solderless conductive circuits ( 50 ) are applied to the electronic contacts of the electronic parts, thereby providing the electronic assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/038,564, filed Mar. 21, 2008; U.S. Provisional Application No.61/039,059 filed Mar. 24, 2008; and U.S. Provisional Application No.61/075,238 filed Jun. 24, 2008, hereby incorporated by reference intheir entirety.

This application is a continuation-in-part application of pending U.S.patent application Ser. No. 12/119,287, ELECTRONIC ASSEMBLIES WITHOUTSOLDER AND METHODS FOR THEIR MANUFACTURE; U.S. patent application Ser.No. 12/163,870, ELECTRONIC ASSEMBLIES WITHOUT SOLDER AND METHODS FORTHEIR MANUFACTURE; U.S. patent application Ser. No. 12/191,544,ELECTRONIC ASSEMBLIES WITHOUT SOLDER AND METHODS FOR THEIR MANUFACTURE;U.S. patent application Ser. No. 12/170,426, ELECTRONIC ASSEMBLIESWITHOUT SOLDER AND METHODS FOR THEIR MANUFACTURE; U.S. patentapplication Ser. No. 12/182,043, ASSEMBLY OF ENCAPSULATED ELECTRONICCOMPONENTS TO A PRINTED CIRCUIT BOARD; U.S. patent application Ser. No.12/187,323 SYSTEM FOR THE MANUFACTURE OF ELECTRONIC ASSEMBLIES WITHOUTSOLDER; and U.S. patent application Ser. No. 12/200,749 ELECTRONICASSEMBLIES WITHOUT SOLDER AND METHODS FOR THEIR MANUFACTURE, herebyincorporated by reference in their entirety.

COPYRIGHT NOTICE AND PERMISSION

This document contains some material which is subject to copyrightprotection. The copyright owner has no objection to the reproductionwith proper attribution of authorship and ownership and withoutalteration by anyone of this material as it appears in the files orrecords of the Patent and Trademark Office, but otherwise reserves allrights whatsoever.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to the field of electronic assembly andmore specifically to the manufacture and assembly of flexible circuitsby molding and plating of electrical and electronic interconnectionswithout the use of solder.

2. Background Art

The assembly of flexible circuits, and more specifically the permanentassembly of package IC components and discrete electronic components(e.g., chip resistors, chip capacitors, diodes, etc.) to the outersurfaces of flexible circuit boards, has involved the use of some formof relatively low temperature solder alloy (e.g., Sn63Fb37) since theearliest days of the electronics industry. The reasons for using solderassembly are numerous, but can be summarized by noting here that it haslong served well to allow for the mass joining of thousand ofelectronics interconnections between printed circuits (rigid orflexible) and the leads of electronic components.

While solder alloys have been most common, other joining materials havebeen proposed and/or used, including isotropic and anisotropic adhesivesor so-called “polymer solders” which are a form of conductive adhesive.In some cases even non-conductive adhesives have also been suggested.Moreover, there have been efforts to make connections separable byproviding sockets for components, to facilitate removal and replacementif needed or desired. In addition, there have also been electrical andelectronic connectors developed to link power and signal carryingconductors with various resilient contact structures, but all of whichrequire constant applied force or pressure.

Adhesive and socket solutions are attractive for some applicationsbecause they do not require exposing components mounted on them to hightemperatures, however, each of these solutions also has limitationsrelated to cost, performance, reliability, and combinations thereof.Current generation adhesives are not as conductive as electronic solderand sockets, while they allow for easy component removal andreplacement. They also add unwanted weight and are expensive.

In recent years the electronics industry has been forced by EuropeanUnion legislation to eliminate the element lead (Pb) from solder, basedon a presumption of risk to humans which has yet to be proven. However,the impact of this legislation has been deleterious to the electronicsindustry as electronic assemblies are less reliable because of thehigher temperatures required. In addition, the energy used to obtain thehigher temperatures has been damaging to the environment. Present daytechnical and trade journals for the electronics industry are repletewith articles and technical papers describing problems associated withlead-free soldering and research into ways to make the problem lessonerous. The high temperatures of soldering significantly reduce thenumber of options available for use as a prospective substrate and tendto force the user to employ higher temperature materials.

Given the aforementioned problems in the assembly of flexible circuitswith solder, especially for lead-free solders, there is room for furtherimprovement in flexible circuit assembly technology.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provideimproved electronic assemblies, especially electronic assembliesdesigned to be flexed for installation or in use.

And it is a further object of the present invention to provide improvedmethods for manufacturing of such electronic assemblies.

Briefly, one preferred embodiment of the present invention is a methodfor the manufacture of a monolithic molded electronic assembly. A moldis provided that has a first mold portion and a second mold potion thatmate together to form an interior chamber, wherein the mold has aninjection port that connects into an injection channel that connectsinto the chamber. A plurality of electronic parts that have electroniccontacts are populated onto the second mold portion, such that theelectronic parts will be substantially contained in the chamber. Thefirst and the second mold potions are then mated together and aninsulating molding material in a liquid state is injected into theinjection port and through the injection channel to fill the chamber.The molding material is hardened from the liquid state to a solid state,thereby embedding the plurality of electronic parts in the moldingmaterial as a monolithic sub-assembly. The monolithic sub-assembly isremoved from the mold and one or more solderless conductive circuits areapplied to the electronic contacts of the electronic parts, therebyproviding the monolithic molded electronic assembly.

Briefly, another preferred embodiment of the present invention is anarticle of manufacture made by the method described in the precedingparagraph.

And briefly, another preferred embodiment of the present invention is acircuit assembly. The circuit assembly includes a plurality ofelectronic parts that have electronic contacts. The electronic parts areover molded with a flexible-hardening insulating molding material to afirst thickness, to have areas between sub-pluralities of the electronicparts having a different second thickness thereby forming a monolithicsub-assembly. And the monolithic sub-assembly has at least onesolderless layer of conductive circuits interconnecting the electroniccontacts of the electronic parts.

These and other objects and advantages of the present invention willbecome clear to those skilled in the art in view of the description ofthe best presently known mode of carrying out the invention and theindustrial applicability of the preferred embodiment as described hereinand as illustrated in the FIGURES of the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The purposes and advantages of the present invention will be apparentfrom the following detailed description in conjunction with the appendedFIGURES of drawings in which:

FIG. 1 depicts a representative assembly method used in accord with thepresent invention to produce an electronic circuit assembly.

In the various FIGURES of the drawings, like references are used todenote like or similar elements or steps.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention is a method for themanufacture of monolithic molded electronic assemblies without solderhaving integral sections which are disposed for flexing when theassembly is complete. This is illustrated in the various drawingsherein, and particularly in the view(s) of FIG. 1, wherein theembodiment of the invention are depicted by the general referencecharacter 10.

In the following description and in the accompanying drawings, specificterminology and drawing symbols are set forth to provide a thoroughunderstanding of the present invention. In some instances, theterminology and symbols may imply specific details that are not requiredto practice the invention. For example, the interconnection betweenconductor elements of components (i.e., component I/O leads orterminals) may be shown or described as having multi-conductorsinterconnecting to a single lead or a single conductor signal lineconnected to multiple component contacts within or between devices.Thus, each of the multi-conductor interconnections may alternatively bea single-conductor signaling, control, power, or ground line and viceversa. Any circuit paths described as being single-ended may also bedifferential, and vice-versa. The interconnected assembly may becomprised of standard interconnections, microstrip or striplineinterconnections and all signal lines of the assembly may be eithershielded or unshielded.

FIG. 1 provides an example of an assembly method 10 used in accord withthe present invention to produce an electronic circuit assembly 12.

In a step A, a mold 14 is provided which has a first mold portion 14 aand a second mold portion 14 b. [N.b., to simplify presentation of theinventive principles here the mold portions are depicted as twoportions, specifically top and bottom ones. It should be appreciated,however, that alternate embodiments of the inventive assembly method 10may employ molds 14 having more then two portions and that orientationas “top” or “bottom” portions is not a requirement.]

When mated together, the first mold portion 14 a and the second moldportion 14 b form an interior chamber 16 inside the mold 14. Thischamber 16 is characterized by having at least two sets of sub-regions18. The chamber 16 shown has two identical thick sub-regions 18 a andone thin sub-region 18 b. Of course, in straightforward manner and aswill become clear as this discussion proceeds, alternate embodiments ofchambers 16 in accord with this invention may have only a single thickregion, say if the electronic assembly requires little flexibility, andyet other embodiments may have a larger number of different sets ofsub-regions, say, ones for particularly thick electronic parts, othersfor various less thick electronic parts, yet others where no electronicparts are placed, and even others where minimal thickness is needed(e.g., for maximum flexibility).

Continuing still in step A, the chamber 16 also has at least one contactwall section 20. In FIG. 1 the mold 14 shown has only one contact wallsection 20 and it is flat and at the bottom of the chamber 16 (i.e., onthe second mold portion 14 b), but alternate embodiments may have morethan one contact wall section on one mold portion or may have one ormore contact wall sections on “other” sides of the chamber 16.

The first mold portion 14 a has at least one injection port 22 forreceiving a liquid mold material, and each such injection port 22connects to one or more injection channels 24 that are suitable for theliquid mold material to flow through into the chamber 16. Additionallyand optionally, the mold 14 may have one or more relief ports (notshown) to allow air (or another ambient gas present during molding) aswell as excess liquid mold material to escape. Alternately, the moldportions 14 a, 14 b may be loosely mated during molding and thus allowair or gas and excess mold material to escape. [N.b., by analogyparticularly to traditional sand casting, the mold 14 as a whole isanalogous to a “pattern,” the first mold portion 14 a is analogous to a“cope,” the second mold portion 14 b is analogous to a “drag,” theinjection port 22 is analogous to a “sprue” or injection ports 22 areanalogous to “runners,” and any relief ports are analogous to “risers.”]

The second mold portion 14 b and the contact wall section 20 aredepicted here as flat, but this is merely coincidental with the use ofthis particular example, and is not a limitation.

In a step B the second mold portion 14 b at the contact wall section 20is populated with electronic parts 30, such as the depicted IC packages30 a and discrete components 30 b (e.g., resistors, capacitors, andinductors or RF coils). The electronic parts 30 are preferably packagedIC's, fully tested and burned-in, and are quality assured discretecomponents to assure their long term reliability in the circuit assembly12 in use. In the embodiment depicted in FIG. 1, gravity may be adequateto hold the electronic parts 30 in place. In other embodiments, however,a more affirmative mechanism may be needed to hold the electronic parts30 in place, if the contact wall section 20 is not horizontally flat orif rapid injection of a molding material might move some of theelectronic parts 30. Then an adhesive or equivalent mechanism may beused to retain the electronic parts 30 in place.

Of course, other parts than those shown can also be employed, and thesemight include connectors, sockets and other interconnection devices ofthat sort. In the example here, the electronic parts 30 are shown placedentirely inside what will be the chamber 16 when the mold 14 is closed,but this also is not an absolute requirement. For example, one end or aribbon cable might be placed inside the chamber 16, in the manner of theother electronic parts 30, while the other end of this ribbon cablemight protrude from the mold 14. The end of the ribbon cable then willalso protrude from the finished circuit assembly 12, in one embodiment,to permit electrical connection of the circuit assembly 12 into anotherelectronic assembly.

Continuing still in step B, the electronic parts inherently haveelectronic contacts 32 (or terminals or pads) and these, for reasonsthat will become clear presently, are usually arranged to be against acontact wall section 20 of the chamber 16.

In a step C, the first mold portion 14 a is about to be mated with thenow parts-populated second mold portion 14 b. In general, step C isstraightforward, but depicting it here serves to show an optionalfeature of the mold 14. For flexibility and robustness of the finishedcircuit assembly 12, optional transition radiuses 34 can be provided inthe mold 14 at some of the edges of the sub-regions 18, as shown. Inaddition to facilitating the flow of a liquid mold material, these canparticularly provide strain gradients in the ultimate circuit assembly12 being produced here.

In a step D, the first mold portion 14 a and the second mold portion 14b have been mated, and an insulating molding material 36 in a liquidstate has been injected into the injection port 22, through theinjection channels 24, and has filled the chamber 16 in the mold 14.

In a step E, the molding material 36 which was in a liquid state has nowbeen hardened to a solid state, thus embedding the electronic parts 30in the molding material 36 and forming a monolithic sub-assembly 40 thatis shown here removed from the mold 14. In particular, it can be seenhere that this monolithic sub-assembly 40 has thick areas correspondingwith the thick sub-regions 18 a of the chamber 16 in the mold 14, a thinarea 44 corresponding with the thin sub-region 18 b, and that theelectronic contacts 32 of the electronic parts 30 that were abutting thecontact wall section 20 of the mold 14 are now exposed at a contact face42. Additionally, this monolithic sub-assembly 40 has material radiuses46 that correspond with the transition radiuses 34 in the mold 14.

In a step F, one or more conductive circuits 50 are formed on to thecontact face 42 of the monolithic sub-assembly 40, thus makingelectrical connections as needed between the electronic contacts 32 ofthe various electronic parts 30. These conductive circuits 50 can bemade by any of a number of different processes, including plating anddirect connection with conductive inks or catalytic inks which can laterbe metalized using an electroless or electrolytic plating process orcombinations of any or all of these. Notably, the process used here canbe a solderless one, with all of the advantages that it entails, and infact, while a solder based process might still be used here, there is nopractical benefit.

Additionally, an optional insulating cover 52 is installed here overpart or all of the exposed surface of the conductive circuits 50. Thisinsulating cover 52 layer can similarly be applied by any suitablemeans, for example, screen printing, photo imaging, or direct printing.While only one layer of conductive circuits 50 and one layer ofinsulating cover 52 are shown for brevity here, multiple layers of bothcan be applied as desired to create more complex circuit assemblies. Atthis point, the monolithic sub-assembly 40 has been completed into thedesired circuit assembly 12.

Finally, although actual fabrication of the circuit assembly 12 wascompleted in step F, manipulating the circuit assembly 12 for the endapplication still remains. Accordingly, in a step G the circuit assembly12 is formed into shape as needed. From FIG. 1 here it can particularlybe seen how some areas of the circuit assembly 12 are rigid while othersare flexible, as well as how the material radiuses 28 facilitate thisand make the circuit assembly 12 more robust.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, andthat the breadth and scope of the invention should not be limited by anyof the above described exemplary embodiments, but should instead bedefined only in accordance with the following claims and theirequivalents.

1. A circuit assembly, comprising: a plurality of electronic parts (30)having electronic contacts (32), said electronic parts (30) being overmolded with a flexible-hardening insulating molding material (36) to afirst thickness and having areas between sub-pluralities of saidelectronic parts (30) having a different second thickness therebyforming a monolithic sub-assembly (40); and, said monolithicsub-assembly (40) having at least one solderless layer of conductivecircuits (50) interconnecting said electronic contacts (32) of saidelectronic parts (30).
 2. The circuit assembly of claim 1, wherein: saidmonolithic sub-assembly (40) further has at least one insulating cover(52) applied over at least part of said at least one solderless layer ofconductive circuits (50).
 3. The circuit assembly of claim 1, whereinsaid electronic parts (30) are packaged prior to said electronic parts(30) being over molded.
 4. The circuit assembly of claim 1, wherein saidelectronic parts (30) are pre-tested and burned in prior to saidelectronic parts (30) being over molded.
 5. The circuit assembly ofclaim 1, wherein said electronic parts (30) are and burned in prior tosaid electronic parts (30) being over molded.